The present invention relates to a method of making cushion materials and more particularly, to cushion materials made, in predetermined forms, of soft polyurethane foam slab and/or chips.
Heretofore, cushion materials for use in automotive seats and home furnitures have been manufactured by using molds of specified shape to expansion-mold a soft polyurethane foam of cellular structure into a predetermined cubic form as shown in FIG. 1(a), or by attaching, as illustrated in FIG. 1(b), a thin polyurethane sheet on the surface profile of a piece already made of soft polyurethane foam as shown in FIG. 1(a). Accordingly, in order to mold cushion materials of different forms, it was necessary to use a special mold and foaming equipment for each of such forms, which resulted in high production costs and wide equipment space. In addition, the prior-art technique needed relatively much labor and time for the manufacture of such cushion products. In the manufacture by expansion molding, occurrence of defects such as protrusions or uneven foaming was unavoidable; also it was necessary to conduct post-treatment like cutting off such protrusions after molding. This also contributed to the high production costs.
The conventional cubic cushion materials include those using rebonded foams by shredding into chips or particles the waste or scrap foam derived from expansion in a mold, applying bonding agent to the chips, and compressing them while curing in reaction with a catalyst or moisture, as disclosed in U.S. Pat. No. 3,114,722; however, these cushion materials are not good in sitting comfort, thus being not suitable for use in automotive seats and quality home furnitures. Furthermore, such cushion material in which polyurethane foam chips or comminuted polyurethane foam particles are bonded and cured by bonding agent is disadvantageous in that the elasticity is not uniform in the whole cushion material and that the foam chips are separated and displaced from each other so that the cushion material is easily deformed.
Further, a method has been also proposed in which a polyurethane foam slab is utilized as cushion material in a seat, the cover of the seat is cubically sewn to make the foam slab comply with cubic form of the seat cover, buttons are provided on the seat cover as needed and pulled down with strings through the foam slab to compress the polyurethane foam slab at said buttons, thereby providing a cushion material in a desired form; compared with a cushion material initially foamed into a cubic form in a mold, however, the above-mentioned cushion material is not good in sitting comfort and durability; also, it is very troublesome to sew and button the seat cover and cushion material for a desired form.
Conventionally, the cushion material for use in the automotive seat is placed on the frame and spring mechanism forming together the seat. A cushion material like this comprises, as shown in FIG. 2, a main body 100 along the peripheral sides of which a side piece 101 is attached. When the cushion material is placed on said frame and spring mechanism of the seat, the side piece 101 encloses the outer periphery of the frame and spring so as to prevent the cushion material from displacing; however, in this example, the process of attaching the side piece 101 is indispensable but it is troublesome, thus decreasing the efficiency of cushion-material production. The foaming equipment can be so operated as to form the bent piece integrally with the main body without attaching the side piece along the peripheral sides of main body 100; however, in case of producing automotive seat cushion materials, it is necessary to use many shapes of molds for different types of the automobile. The conventional method of making cushion materials is thus disadvantageous also from the standpoint of equipment space in the factory.